Crystals morphology of AFO-type structure AlPO4-41 and SAPO-41 molecular sieves

Abstract Morphology of AFO-topology molecular sieves has been identified from the large individual crystals of AlPO 4 -41 and SAPO-41, which were synthesized from three routes: (1) using H 3 PO 3 as the phosphorus source; (2) the mixture of H 3 PO 3 and H 3 PO 4 being used as the phosphorus source; (3) an aluminophosphite NKX-2 used as the aluminum and phosphorus source, respectively. Shape clear large individual crystals of AlPO 4 -41 with the aspect ratio being 3.0 have been obtained from the in situ transformation of NKX-2. It has been found that H 3 PO 3 -containing systems not only favor the formation of AFO-structure molecular sieves, but also promote the growth of their large crystals. The crystal morphology of AlPO 4 -41 has been identified as octagonal prisms. Furthermore, SAPO-41 crystals with lower aspect ratio (being 0.25) have been obtained. It is notable that if silicon is incorporated in the AFO framework, further crystallization may be hindered, resulting in the formation of plate-like crystals just similar to what happened in AFI-structure. Besides, as the aspect ratio decreases, the diffraction intensities of planes in XRD patterns such as (1 0 0), (0 2 0) (2 1 0), and (1 3 0) decrease, whereas the intensity of (0 0 2) increases remarkably.